JPH046778B2 - - Google Patents

Description

[Detailed description of the invention]

<Industrial Application Field> The present invention relates to a fluidized bed reduction method for powdery ore containing metal oxides, and particularly to a method for stably fluidizing and efficiently reducing fine powder ore. <Conventional technology> Most metal oxides such as iron ore are extracted as underground resources in the form of powder rather than lumps, and it is expected that the number of powder ores will increase further in the future. Currently, most of the fine ore used as a raw material for sintering is sinter feed, which has an average particle size of around 1 mm, but its supply is gradually decreasing, and in the future, it will become smaller than this. The average particle size is 0.3 mm or less, and the size is 325 mesh (0.044 mm).
There is a tendency for the amount of so-called pellet feed, which contains a considerable amount of less than 1 mm), to be supplied. In principle, the particle size of the ore to be reduced is small, but the thermal efficiency and reducing gas utilization efficiency are high. Therefore, in the process of metal smelting, it is becoming necessary to use such powdered ores directly due to raw material conditions. On the other hand, directly using such powdered ore to smelt metal is advantageous in terms of energy saving and manufacturing cost. Conventionally, the technology for directly using sintered ore powder with an average particle size of around 1 mm is to pre-reduce the powder ore using a fluidized bed, and then turn this pre-reduced ore into agglomerates. The ferroalloy manufacturing technology that does not require electric power is the method of smelting and reducing in electric furnaces, converters, and other melting furnaces, or the recently developed ferroalloy manufacturing technology that does not require electricity, using equipment that combines a fluidized bed pre-reduction furnace and a rigid smelting and reduction furnace. There is a method of pre-reducing powdered ore and directly producing ferroalloy without an agglomeration process. In particular, when iron ore pre-reduced in a fluidized bed pre-reduction furnace is injected into a vertical smelter-reduction furnace containing two upper and lower tuyere stages as disclosed in Japanese Patent Publication No. 59-18453, iron ore pre-reduced in a fluidized bed pre-reduction furnace is smelted and reduced. , the melt reduction rate between the upper and lower tuyeres influences the unreduced FeO concentration, and for pre-reduced fine ore with the same reduction rate, the smaller the particle size, the higher the melt reduction rate in the melt between the upper and lower tuyeres. It is expected that the FeO concentration will be lower and the reactivity with the furnace wall refractories will also be reduced, reducing erosion of the furnace wall refractories. Figure 3 shows the pre-reduced ore particle size and the difference between the upper and lower tuyeres when experimentally produced pre-reduced iron ores with various particle sizes were blown into a vertical smelting reduction furnace and smelted and reduced. It shows the relationship between the FeO concentration in the melt, and under the same reduction rate, there is a positive correlation between the particle size and the FeO concentration. In other words, the smaller the particle size of the pre-reduced ore, the lower the FeO concentration between the upper and lower tuyeres, which reduces erosion of the furnace wall refractories, and at the same time speeds up the melting reaction in the smelting reduction furnace, improving productivity. can. From this point of view as well, it is desired to develop a fluidized reduction method that can use fine ore having a smaller particle size. Conventionally, the following (1) to (5) can be considered as the main conditions required for a fluidized bed as an ore reduction furnace. (1) It is easy to supply heat to maintain the reaction temperature to obtain the required reduction rate. (2) Fluidization will not be inhibited due to sintering caused by local heating or adhesion of the pre-reduced ore at high temperatures. (3) A uniform and stable fluidization phenomenon should be obtained. (4) The required reduction rate can be obtained even with a short residence time. (5) Less dust is generated due to particles flying out of the fluidized bed. Based on this idea, the fluidization conditions for coarse particle systems such as sinter feed were performed by setting the flow rate of the fluidizing gas to 2 to 3 times the fluidization start speed and performing fluidization reduction. . However, under these fluidization conditions, the average particle size
When fine ore such as pellet feed containing a considerable proportion of fine ore of 0.3 mm or less and 0.044 mm or less was subjected to fluidized bed reduction, the following problems occurred. That is, (1) As a characteristic of fine powder ore, the cohesive force between particles is strong and the contact between particles and reducing gas is poor, and depending on the fluidization conditions, it is not always possible to obtain the required reduction rate and productivity does not improve. (2) More particles fly out from the fluidized bed, and when combined with the dust in the fluidizing gas generated from, for example, a smelting reduction furnace, a large amount of dust is generated, resulting in a significant decrease in yield. (3) Because the particle size is small, sintering of the pre-reduced ore tends to occur and fluidization is inhibited. <Problems to be Solved by the Invention> The present invention solves the following problems in the fluidized bed reduction method of fine ore called pellet feed: (1) reduction in productivity due to agglomeration between particles; (2) drop in productivity due to particles flying out of the fluidized bed. A fluidized bed that solves problems such as a decrease in distillation and (3) inhibition of fluidization due to sintering of particles, overcomes the raw material situation, and fully utilizes the inherent high thermal efficiency and reducing gas utilization efficiency of fine ore. This is an attempt to provide a method for giving back. <Means for solving the problem> The present invention is directed to an ore having an average particle size of 0.3 mm or less,
And the content of ore with a particle size of 0.044 mm or less is 10 ^wt %
When the above powdered ore is fluidized and gas-reduced in a fluidized bed reduction furnace, the particle size of the powdered ore is
Depending on the content R ( ^wt %) of 0.044 mm or less, the particle layer density D _F (Kg/m ³ ) in the fluidized tank is controlled within the range of 20000・R ^-1.4 ≦D _F ≦7000・R ^-0.67 . The present invention provides a fluidized bed reduction method for fine ore, which is characterized by reducing fine ore. <Function> FIG. 4 is a schematic diagram of a fluidized bed reduction apparatus suitably used in carrying out the present invention. 1 is a fluidized bed reduction furnace, and fine ore is introduced into a hopper 4, cut out by a discharge device 5, and continuously supplied to the fluidized bed reduction furnace 1 by a screw feeder 6. Next, the fluidized reducing gas is discharged from the reducing gas supply equipment (not shown) or from the smelting reduction furnace when the fluidized bed reduction furnace is used as a pre-reduction furnace for supplying pre-reduced ore to another smelting reduction furnace. The high-temperature reducing exhaust gas is introduced into the fluidized bed reduction furnace 1 via a duct 9 either as it is or with its temperature controlled by a reducing gas temperature adjustment device 8 . Reference numeral 10 denotes a fluidizing gas amount adjusting device that controls the flow rate of the fluidizing gas, and excess gas is discharged as exhaust gas. 7 is a dispersion plate. 14 is a differential pressure detection device, 15 is a calculation device, and the particle bed density is determined by the calculation device 15 based on the differential pressure ΔP of the fluidized bed detected by the differential pressure detection device 14.
D _F is calculated, and based on the signal, the fluidizing gas amount is adjusted by the fluidizing gas amount adjusting device 10 so that D _F becomes the target value. On the other hand, particles and dust ejected from the fluidized bed reduction furnace 2 are collected by the cyclone 3, and are collected by the circulation pipe 1.
1, and is continuously returned to the fluidized bed reduction furnace for fluidized bed reduction. Next, the pre-reduced ore is cut out by the pre-reduced ore cutting device 13 via the pre-reduced ore discharge pipe 12 which branches from the middle of the circulation pipe 11 when the reduction rate reaches a predetermined value. The particle bed density D _F (Kg/m ³ ) is the value obtained by dividing the charge amount (Kg) in the fluidized bed by the internal volume (m ³ ), but from a macroscopic perspective, it is the differential pressure of the fluidized bed. ΔP(N/
m ² ) and the height Δh (m) between the differential pressure detection positions as shown in the following equation, so by detecting the differential pressure ΔP,
easy to know. However, g is gravitational acceleration (m/sec ² ). D _F = ΔP/(Δh・g) On the other hand, D _F depends on the fluidizing gas flow rate, ore supply rate, temperature in the tank, pressure in the tank, etc. during operation, but it can be adjusted by adjusting the fluidizing gas flow rate. It is easiest to control the The reason why the particle bed density D _F contributes to operational stability is that if D _F is excessively large, the amount of fluidizing gas is too small relative to the amount of ore, resulting in poor fluidization and poor contact efficiency with the reducing gas. Also, if D _F is too small, there will be too much fluidizing gas, which will cause more particles to fly out and reduce the utilization rate of reducing gas. ,
It is thought that productivity will decrease. Next, as an example, we conducted an experiment in which the particle bed density in the fluidized bed was changed by controlling the flow rate of the fluidizing reducing gas using fine ore containing about 70% fine ore with a particle size of 0.3 mm or less and 0.044 mm or less. Explain the results. As shown in Figure 2, the relationship between the particle bed density in the fluidized bed and the productivity of pre-reduced ore is that for fine ore in which 70% of the particles have a particle size of 0.044 mm or less, the productivity decreases when the particle bed density is 400 Kg/ ^m3 or more. On the other hand, between 50 and 400 Kg/m ³ , fluidization is good and productivity is good, but below 50 Kg/m ³ , fluidization, that is, contact efficiency with reducing gas is good, but
The number of particles flying out increased, the utilization rate of reducing gas decreased, and productivity decreased. Table 2 shows a comprehensive comparison of the particle layer density and each property of fine ore with 70% of 0.044 mm or less, and shows that the optimum particle layer density is 50 to 400 kg/ ^m3 . I found it.

[Table] Furthermore, the appropriate particle bed density range within the fluidized bed changes depending on the content of ore with a particle size of 0.044 mm or less. Figure 1 shows the relationship between the content of 0.044 mm or less and the particle layer density in an appropriate fluidized bed.If the particle layer density is outside the appropriate range, poor fluidization and particles flying out will increase, and the gas utilization rate will increase. When reducing fine ore containing 10% or more of ore of 0.044 mm or less, which is the object of the present invention, D _F must be controlled within the range of 20000・R ^-1.4 ≦D _F ≦7000・R ^-0.67 as shown in the figure. Must be. On the other hand, when the content of 0.044 mm or less is 10% or less, the appropriate particle layer density is 800~
It becomes constant within the range of 1500Kg/ ^m3 . This is because the particle size has approached that of a coarse particle system. However, the finding that the appropriate particle layer density in the fluidized bed changes depending on R in a range where the content R of fine powder of 0.044 mm or less, which is more fine than this, is 10% or more is completely new. . <Example/Comparative Example> Using a fluidized bed reduction furnace with a furnace inner diameter of 1.0 m, the first sample containing 66.3% of particles with an average particle size of 0.3 mm or less and 0.044 mm or less was prepared.
700-800Kg/H of fine iron ore with the particle size composition shown in the table.
The particle layer density was (A) 50 Kg/m ³ , (B) 200 Kg/m ³ , and the exhaust gas at around 1000°C from the smelting reduction furnace was controlled at 750 to 800°C as the fluidizing blast gas.
(C) Three levels of 1000Kg/m ³ were set and productivity was compared.

【table】

[Table] The results are as shown in Table 3, with a particle density of 50 (Kg/
m ³ ), the protrusion from the cyclone was large and the gas utilization rate was low, so productivity was not sufficient. In addition, in the case of 1000 (Kg/m ³ ), the utilization rate of the reducing gas is good and the splashing out from the cyclone is small, but the adhesion between particles occurs frequently and fluidization is inhibited, making it impossible to perform stable reduction. However, productivity was still not sufficient. On the other hand, in the case of 200Kg/ ^m3 , which is within the scope of the present invention, there is less adhesion of particles, the fluidized bed is stabilized, and the gas utilization rate is good.
50 (Kg/m ³ ) and 1000 (Kg/m ³ ), the productivity is approx.
A good productivity of 12 tons/day was achieved, which was an improvement of 30%. In this experimental example, an example of iron ore was shown, but Ni ore,
The present invention was similarly applicable to Cr ore, Mn ore, and the like. <Effects of the invention> The present invention makes it possible to stabilize fine ore containing a considerable amount of fine ore with an average particle size of 0.3 mm or less and with a particle size of 0.044 mm or less, which was conventionally difficult to use in a fluidized bed reduction furnace. As a result, production can be increased and energy consumption reduced. Furthermore, when pre-reduced iron ore produced in a fluidized bed reduction furnace is charged into a smelting reduction furnace and smelted and reduced, it is possible to supply pre-reduced iron ore with a smaller particle size, making it possible to reduce the amount of iron ore in the melt. This has the effect of reducing the FeO concentration and reducing erosion of the furnace wall refractories of the smelting reduction furnace.

[Brief explanation of drawings]

Figure 1 shows the content of 0.044 mm or less and the appropriate particle layer density, Figure 2 shows the relationship between the particle layer density in the fluidized bed and productivity, and Figure 3 shows the pre-reduced ore particle diameter. FIG. 4 is a diagram showing the relationship between the FeO concentration in the melt between the upper and lower tuyeres, and FIG. 4 is a diagram showing the fluidized bed pre-reduction apparatus according to the present invention. 1...Fluidized bed preliminary reduction furnace, 3...Cyclone,
3... Fine ore hopper, 6... Screw feeder, 7... Dispersion plate, 8... Reducing gas temperature control device, 10... Fluidization gas amount control device, 13... Preliminary reduced ore cutting device, 14 ...Differential pressure detection device, 1
5...Arithmetic device.

Claims (1)

[Scope of Claims] 1. An ore with an average particle size of 0.3 mm or less, and
When powdered ore containing 10 ^wt % or more of ore with a particle size of 0.044 mm or less is fluidized and gas-reduced in a fluidized bed reduction furnace, the particle layer density D _F (Kg/m ³ ) of the fluidized bed is set to the particle size of 0.044 mm in the ore. A fluidized bed reduction method for fine ore, characterized by controlling the reduction within the range of the following formula according to the content R ( ^wt %) of fine ore of less than mm. Note 20000・R ^-1.4 ≦D _F ≦7000・R ^-0.67